As is too common and a bit frustrating there isn't much information about the methods they intend using and certainly not a glimpse of their business plan.
Sounds like the intention is to use a vaporising and separating method of PGM extraction, which I wasn't aware of as a commercial process - or as something applied to nickel-iron for this purpose. Electric arc rather than laser (lasers being very energy inefficient as a heating method) is my guess. I had been expecting Mond process - "dissolving" in carbon monoxide gas and vapor deposition, used commercially for extracting nickel, that has been proposed as a refining method for asteroid Ni-Fe, however I wonder if it actually works the way I had thought (separation of nickel and iron leaving a residue of the rest, rich in cobalt and PGM's). Some lab somewhere has likely tried it with metal meteorites but I haven't found examples. But how the mining and refining is done is still only a part of the whole exercise.
Much as they appear to have the most nickel-iron, therefore most PGM's, asteroids don't have to be M-class to have a lot of nickel-iron. Ni-Fe is very abundant, although there are variations in PGM concentrations - different Ni-Fe alloys, with higher PGMs are linked with higher nickel content. The extent to which they are found separately isn't clear.
I'm inclined to favour C-class carbonaceous asteroids that are likely to have an abundant sufficiency of Ni-Fe as grains and nodules within a softer carbonaceous matrix - for the ability to make the other things asteroid mining needs, things like rocket fuel, that I would expect to be the single largest ongoing "consumable" required.
Transport costs are what makes doing things in space so expensive; typically many times more rocket fuel than payload. I do think the efficiency and cost of the rocketry is crucial to the economics and the ability to produce fuel on-site seems crucial to cutting costs. M-class asteroids seem less likely to have the means to make rocket fuel or chemical feedstocks for more complex refinining methods and/or making the machinery and equipment on-site.